The invention relates to the projection of picture slides or diapositives onto a viewing screen. It is known in the art to use two separate projectors with separate magazines, for projecting pictures onto the same viewing screen with a lap-dissolve effect the picture from one projector fading out as the picture from the other projector becomes visible, thus producing a pleasing change of scene without an intervening interval of darkness or of brightly illuminated screen with no picture on it. The objection to such an arrangement is that the slides in the magazine of one projector must be very carefully placed with relation to the slides in the magazine of the other projector, in order to project the pictures in the desired sequence.
It is also known to use twin projectors fed from a single magazine, with the advantage that the slides can be arranged in the magazine exactly in the desired order of projection, avoiding the extra trouble of having to correlate slides in one magazine with those in another. An example of this arrangement is Carrillo U.S. Pat. No. 3,093,030 of June 11, 1963. The disadvantage of this arrangement is that the slides must be fed by hand, rather than mechanically, and that the slides are not returned to the magazine after projection, so that they must be manually rearranged in the magazine before the next projection sequence. Another example of twin projectors fed from a single magazine is Sobotta U.S. Pat. No. 3,847,472, granted Nov. 12, 1974. This has the advantage of depositing the slides back into the magazine in proper sequence, but the disadvantage of a somewhat complicated and expensive construction with picture gates that move axially forwardly and backwardly from loading position to projection position and vice versa.
The two closely related patents of Floden, U.S. Pat. Nos. 3,462,215 of Aug. 19, 1969, and Jackson, 3,501,232 of Mar. 17, 1970, disclose other arrangements for feeding successive slides from a single magazine alternately to two separate projection gates, and then returning the slides in proper sequence to the same magazine. However, the constructions shown in these two patents cannot be used for lap-dissolve operation, and also cannot be used for either panoramic viewing or stereoscopic viewing of two pictures projected side by side.
Another example of a dual projector system is the patent of Grenier, British Pat. No. 1,158,150, published July 16, 1969. In this patent, slides from the same magazine are fed to the two projection gates, and there is provision for lap-dissolve operation, and also for panoramic operation and for stereoscopic operation. However, the feeding and recovery of the slides must be performed by hand, and there is no disclosure of any way of providing for motor driven operation.
An object of the present invention is the provision of an improved dual slide projector which overcomes the difficulties or drawbacks above mentioned, and which provides for motor driven operation in any one of three modes, either with fade-in-fade-out or lap-dissolve projection of successive pictures onto the same area of the viewing screen, or for panoramic projection of separate pictures in side-by-side relation on the viewing screen, or for stereoscopic projection of related stereoscopic pairs of pictures onto the same area of the viewing screen, using appropriate polarizing means or other stereoscopic devices as well understood in the art.
Another object of the invention is to provide such a dual projector of the kind just mentioned, having provision for quick and easy changeover from one mode to another mode of operation, the slides in all modes of operation being taken successively from a single magazine, and after projection, being returned to that magazine in the original sequence, so that the magazine is immediately ready for reuse in another projection operation, without having to rearrange the slides in the magazine.
Still another object is to provide such a dual projector of relatively simple design, comparatively inexpensive to manufacture, and trouble-free and sturdy in use.